The maximum allowable constant electrical current rating having to meet the design, security and safety criteria, such as electrical clearance, of a particular power line on which an electrically conductive cable is used is known under the term “ampacity”, as described for instance in “Sag-tension calculation methods for overhead lines”, published in 2007 as CIGRE Technical Brochure No. 324 by Study Committee B2 of the International Council on Large Electric Systems (CIGRE).
Power line rating (i.e. ampacity) can be dynamically estimated using smart sensors. The so-called dynamic line rating is nowadays considered with great interest in everyday operation of power networks all around the world. Forecasted values of ampacity are also used in day-ahead network management as well in several days ahead network market approach, while even very long term approach may be used for planning. Medium- and long-term, i.e. over about four hours, forecasted values are based on forecasted meteorological data whereas real-time and short-time ampacity forecasts are based on real-time and possibly short past analysis of actual conditions acting on the power lines, like time series. Those conditions, including wind speed, wind direction, and ambient temperature for example may be locally measured, computed or inferred from actual observations on or near the field. Most generally, measurements, computations and actual observations may be combined by appropriate stochastic tools to deduce the forecasted power line rating values.
Methods to evaluate the ampacity of a suspended/anchored cable span on the basis of various data are explained for instance in A. Deb, “Power line ampacity system”, published in 2000 by CRC Press, and in technical brochures from international organizations, such as CIGRE Technical Brochures No. 207 (“Thermal behavior of overhead conductors”) and No. 498 (“Guide for application of direct real-time monitoring systems”), respectively published in 2002 and 2012, as well as in abovementioned CIGRE Technical Brochure No. 324. The methods disclosed in these documents use weather data as locally measured or simulated following international recommendations as explained, for example, in CIGRE Technical Brochure No. 299 (“Guide for the selection of weather parameters for bare overhead conductor ratings”), published in 2006 or IEEE Standard 738-2006—IEEE Standard for Calculating the Current-Temperature of bare Overhead Conductors, published in 2007.
The ampacity calculation is also based on the ruling span concept which allows to replace a full multi-span section by one equivalent so-called “ruling span” which is theoretically giving access to all individual span behaviors but many hypotheses lie behind that theory (Kiessling et al, “Overhead power lines”, Springer 2003, page 548).
Thus, all existing models so far usually use the ruling span concept coupled with the state change equation (Kissling et al, ibid., page 546) and thermal equations including meteorological data, conductor data, sagging conditions, etc.
As explained in U.S. Pat. No. 8,184,015, continuous monitoring of electrical power lines, in particular high-voltage overhead lines, is essential to timely detect anomalous conditions which could lead to a power outage. Measurement of the sag of power line spans between successive supports to determine whether the sag is greater than a maximum value has become a mandatory requirement in some countries.
U.S. Pat. No. 8,184,015 discloses a device and method for continuously monitoring the sag on a power line span. This method allows the determination of mechanical dynamic properties of the power lines just by sensing mechanical vibrations in a frequency range from 0 to some tens of Hertz. Indeed, power lines in the field are always subject to movements and vibrations, which may be very small but detectable by their accelerations in both time and frequency domains.
A number of different methods to measure the sag of a suspended/anchored cable span are also known. An example of tentative sag measurement consists in the optical detection of a target clamped on the monitored conductor by a camera fixed to a pylon, as disclosed in U.S. Pat. No. 6,205,867. Other examples of such methods include measurement of the conductor temperature or tension or inclination of conductor in the span. A conductor replica is sometimes attached to the tower to catch an assimilated conductor temperature without Joule effect.
Besides the fact that these methods only allow a partial monitoring of the power line, such methods suffer from other drawbacks: optical techniques are sensitive to reductions of the visibility induced by meteorological conditions while the other measurement methods depend on uncertain models and/or data which may be unavailable and/or uncertain, e.g. wind speeds, topological data, actual conductor characteristics, etc.
U.S. Pat. No. 5,933,355 discloses a software to evaluate ampacity of a power line. It is based on a thermal model and the ruling span concept.
U.S. Pat. No. 6,205,867 discloses a power line sag monitor based on inclination measurement. It is based on a thermal model and the ruling span concept.
International Publication No. WO 2010/054072 is related to real-time power line rating. It alleges the existence of a sensor about wind speed direction and amplitude but does not disclose how these sensors are constituted. It is based on a thermal model and the ruling span concept.
U.S. Patent Appl. Publ. No. 2014/0180616 is related to power line rating and is using conductor temperature sensor to calibrate IEEE theoretical model, based on actual observations of clearance by LIDAR and conductor temperature spot measurements. It relates to these two values by a linear regression. It is based on IEEE model correction and thus needs all data related to IEEE model, including conductor data, meteorological data and sagging data.